The main purposes of lubrication are to reduce friction and wear in the contact areas as direct metallic contact between the bearing ring , rolling elements and cage is prevented by an oil film. Therefore, the effects of lubrication may be briefly explained as followings:

1. Reduction of friction and wear.
2. Extension of fatigue life.

The fatigue life of bearings depends greatly upon to the viscosity and film thickness of oil between the rolling contact surfaces.

1. Circular lubrication may be used to carry away frictional heat or heat transferred from outside to prevent the bearing from overheating and the oil from deteriorating.
2. Adequate lubrication also helps to prevent foreign material from entering the bearing and to prevent bearings from corrosion or rusting.

Lubricating methods and lubricants
In general, lubricating methods are divided into oil or grease lubrication Oil lubrication

1. Suitable for extremely high operating speed.
2. Good for assembly where the bearings are located in the same housing with oil lubricated components.
3. Suitable for extremely high operation temperatures.
4. Good where a central oil system is used for auxiliary machine parts.
5. Good where bearings torque requirements are a consideration.

Grease lubrication

1. Grease may be retained in a bearing without an elaborate enclosure.
2. Grease give long service without renewal or inspection.
3. Grease increases the effectiveness of dirt exclusion in the enclosure.
4. Enclosed sealed bearing are lubricated at the factory.

As a general rule, bearings should be only filled with from 30%-60% of the free internal space inside bearings. More than the normal amount of grease can cause heat generation or grease leakage.
Based on customer's requirement the grease usually used by E&B listed in table 6.1

Table 6.1 A Detail list of commonly-used lubricating grease